Coverage and channel characteristics of millimeter wave band using ray tracing

Utilization of millimeter wave (MMW) bands for supporting very high data rate cellular access has received much attention in recent times. The behavior of the wireless channel in these bands differ significantly from the sub-6 GHz counterparts. Ray tracing is a complementary effort to detailed measurements in providing quick insight into the coarse channel characteristics. In this paper, we model the 28 GHz outdoor channel through ray tracing using the WinProp tool. We simulate the single base station and multi base station scenarios in the downtown Manhattan area and study channel properties such as coverage and path loss, path diversity and delay spreads. We observe that a typical MMW base station provides coverage to a significant fraction of a 100m cell radius with path diversity, i.e. there exist secondary paths that may sustain the link on the failure of the first path. The improvements to coverage and path diversity with multiple base stations are also characterized. The above channel properties are compared with NYU's [4] results from the same region. We observe a reasonable match for many of the above parameters. The delay spreads with omni and beamformed antennas are also compared. The typical RMS delay spread in a beamformed scenario is seen to be in the order of 20-30 ns which is significantly smaller than the measured values of 100ns or more. This phenomenon is likely due to detailed clutter in the environment not being modeled.